Thin film transistor array panel

ABSTRACT

A semiconductor device comprises a multi-layered structure disposed over a substrate and defining a composite lateral etch profile. The multi-layered structure includes a lower sub-layer disposed over the substrate and comprising a metal oxide material that includes indium and zinc, the indium and zinc content in the bottom sub-layer substantially defining a first indium to zinc content ratio; a middle sub-layer disposed over the bottom sub-layer and comprising a metal material; an upper sub-layer disposed over the middle sub-layer and comprising a metal oxide material that includes indium and zinc, the indium to zinc content in the upper sub-layer substantially defining a second indium to zinc content ratio smaller than the first indium to zinc content ratio; and a lateral byproduct layer formed over the lateral etched surface, comprising substantially an metal oxide of the metal material in the middle sub-layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional applications Ser.No. 62/278448, 62/278467, and 61/278,469 filed on Jan. 14, 2016, and62/311366 filed on Mar. 21, 2016, which are incorporated herein byreference.

FIELD

The subject matter herein generally relates to display technology,pertains particularly to thin film transistor (TFT) array panel.

TECHNICAL FIELD

In flat panel display devices, thin film transistors (TFT) are used asswitching elements for pixel electrodes. A low profile display paneldevice commonly comprises a gate line arranged to transfer a scanningsignal for controlling the thin film transistor and a data line arrangedto transfer a signal applied to the pixel electrode, among others.Research efforts have been devoted in an attempt to enhance signalconducting capability for achieving higher panel device performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 illustrates a schematic planar layout of a portion of a thin filmtransistor (TFT) array panel in accordance with some embodiments of theinstant disclosure.

FIG. 2 shows a cross sectional view of a TFT device in an exemplaryarray panel in accordance with some embodiments of the instantdisclosure.

FIGS. 3A-3D illustrate different schematic etch profiles in amulti-layered conductive layer undergone a patterning process.

FIG. 4 shows a cross sectional view of a TFT device in an exemplaryarray panel in accordance with some embodiments of the instantdisclosure.

FIGS. 5A-5G illustrate an exemplary TFT device in accordance with someembodiments of the instant disclosure at various stages of fabricationprocess.

FIGS. 6A-6C are microscopic cross sectional pictures showing lateraletch profiles in various exemplary second conductive layers.

FIGS. 7A-7C are schematic diagrams illustrating potential effects due tothe lateral byproduct layer profile.

FIGS. 8A-8B are schematic cross sectional illustrations of exemplarysemiconductor devices in accordance with some embodiments of the instantdisclosure.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts may beexaggerated to better illustrate details and features. The descriptionis not to be considered as limiting the scope of the embodimentsdescribed herein.

The term “coupled” is defined as connected, whether directly orindirectly through intervening components, and is not necessarilylimited to physical connections. The connection can be such that theobjects are permanently connected or releasably connected. The term“substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. For example, substantiallycylindrical means that the object resembles a cylinder, but can have oneor more deviations from a true cylinder. The term “comprising,” whenutilized, means “including, but not necessarily limited to”; itspecifically indicates open-ended inclusion or membership in theso-described combination, group, series and the like.

For consistency purpose and ease of understanding, like features areidentified (although, in some instances, not shown) with like numeralsin the exemplary figures. However, the features in different embodimentsmay differ in other respects, and thus shall not be narrowly confined towhat is shown in the figures.

FIG. 1 illustrates a schematic planar layout of a portion of a thin filmtransistor (TFT) array panel in accordance with some embodiments of theinstant disclosure. The schematic illustration of FIG. 1 shows a portionof an exemplary TFT array panel that comprises a [3×5] matrix of TFTpixel elements 10. Each pixel element 10 comprises a TFT switchingdevice 100 and a pixel electrode 120. A TFT switching device (e.g,device 100) is as special type of low profile field effect transistormade by thin films of semiconductive, conductive, and dielectric layers.The thin films of different materials are commonly disposed over asupporting structure, e.g., a non-conductive substrate (not separatelylabeled). The TFT device 100 is generally a three-terminal element thatcomprises a gate electrode 102 and a pair of functionallyinterchangeable source and drain electrodes 105 a/b. The pixel electrode120 is configured to provide liquid crystal (not shown in instantfigure) control in a display panel. The pixel electrode 120 is coupledto one of the source/drain terminals (e.g. terminal 105 b) of the TFTdevice 100. The TFT device 100 functions as a switch that selectivelyturns the connected pixel electrode 120 on and off, thus controls theflow of charge carriers (e.g., holes or electrons) into the pixelelectrode region.

The matrix of pixel elements 10 are interconnected through a network ofsignal conducting lines, which may include a plurality of gate lines 111(shown to be traversing transversely along the page) connecting the gateterminals (e.g, terminal 102) its a row, and a plurality of data lines112 (traversing longitudinally along the page) connecting one of thesource/drain terminals (e.g., terminal 105 a) of the TFT devices 100 ina column. Structurally, the gate lines 111 and the data lines 112 may beformed by one or more patterned conductive layers disposed over thesubstrate. To conserve precious planar area budget on a substrate, thegate lines 111 and the data lines 112 may be arranged at differentelevations (i.e., vertical level) over the substrate in an overlayingfashion. For instance, a signal conducting line may comprise aconductive layer arranged over a substrate and traversing laterally(e.g., in the planar direction over the major surface thereof) between afirst region and a second region.

The gate line 111 may be used to signal communicatively connect the ITTdevice 100 with a gate line driver IC located at a first planar regionon the substrate (not shown). The data lines 112, on the other hand, maysignal conductively couple the TFT device 100 to a source fine driver IClocated at another planar region defined over the substrate (not shown).In a modern flat panel display, the thin film transistor (TFT) arraypanel may comprise thousands or even millions of TFT pixel elements 10arranged in a high dimension matrix to provide high image resolution.

As the network of signal conducting lines are responsible fortransmitting control signals between the pixel elements and the controlICs, the signal conducting capability of the signal conducting linesplays an important role in dictating the performance of the flat paneldisplay device, especially for large size and/or high definition deviceapplications. By way of example, allocation of precious planar area on asubstrate would be required for the conductive lines. to achieve highpixel density while maintaining device performance, the width in theconducting lines may require miniaturization, while the electricalresistance/impedance thereof ought to be reduced.

FIG. 2 shows a cross sectional view of a semiconductor device in anexemplary array panel in accordance with some embodiments of the instantdisclosure. Particularly, FIG. 2 shows a cross sectional view of anexemplary semiconductor device (e.g., TFT device 100) across both thesource and the drain terminals (e.g., S/D electrodes 105 a, 105 b). TheTFT device 100 is disposed on a major surface of a substrate 101 thatprovides structural support. The substrate 101 typically comprises aninsulating material. Suitable materials for the substrate 101 mayinclude glass, quartz, and plastic having sufficient opticaltransparency (e.g., for electromagnetic radiations in the visiblespectrum for visual display applications). In some embodiments, thesubstrate 101 may comprise ceramic and/or materials. In someapplications, flexible substrate materials may be adopted. Suitablechoice of material for the flexible substrate may include, for example,polyethersulfone (PES), polyethylenenaphthalate (PEN), polyethylene(PE), polyimide (PI), polyvinyl chloride (PVC), polyethyleneterephthalate (PET), and stainless steel, or combinations thereof.

The exemplary ITT device 100 comprises a first conductive layer 102disposed over the major surface of the substrate 101, an active channellayer 104 disposed Over the first conductive layer 102 and insulatedthere-from by an insulating layer 103. and a second conductive layer(e.g., the layer that defines the electrodes 105 a, 105 b) disposed overthe channel layer 104 and in electrical contact there-with. The firstconductive layer 102 disposed over the substrate 101 may be patterned toform an array of first level signal conducting lines, For instance, thefirst conductive layer 102 may be patterned to form a first level signalconducting array/network over the substrate 101 (e.g., gate lines 111 asshown in FIG. 1), with portions thereof traversing planarly between afirst region (e.g., the gate region of a TFT device 100) and a secondregion (e.g., a gate line driving IC) define on the substrate. In someembodiments, portions of the first conductive layer 102 may be patternedto define the gate electrodes of the TFT device 100 (e.g., the gateterminal as shown, in FIG. 1). The integrated signal conducting line(e.g., the gate lines) and the TFT device's gate terminal (e.g., thegate electrode 102) may reduce device complexity (and thus fabricationcomplexity). The first conductive layer 102 may selectively comprisealuminum (Al), silver (Ag), gold (Au), cobalt (Co), chromium (Cr),copper (Cu), indium (In), manganese (Mn), molybdenum (Mo), nickel (Ni),neodymium (Nd), palladium (pd), platinum (Pt), titanium (Ti), tungsten(W), zinc (Zn), other suitable conductive materials, and a suitablemixture/alloy thereof. For achieving higher optical efficiency, in someembodiments, the first conductive layer 102 may include a transparentconductive material, such as indium tin oxide (ITO), indium zinc oxide(IZO), aluminum doped zinc oxide (AZO), or a suitable combinationthereof.

The insulating layer 103 may be provided over selective regions of thefirst conductive layer 102 to structurally protect the gate electrode102 (and/or the first level signal conducting lines) and electricallyshield the gate region of the TFT device 100 from shorting with otherdevice features. The insulating layer 103 may selectively comprise asuitable dielectric material, such as silicon oxide (SiOx), siliconnitride (SiNx), silicon oxynitride (SiOxNy), aluminum oxide (AlOx),yttrium oxide (Y2O3), hafnium oxide (HfOx), zirconium oxide (ZrOx),aluminum nitride (AlN), aluminum oxynitride (AlNO), titanium oxide(TiOx), barium titanate (BaTiO3), lead titanate (PbTiO3). In someembodiments, one or more high-I(dielectric material may be used as gateinsulator for the TFT device 100. High-K dielectric materials mayinclude, for example, oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf, Al,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixturesthereof. A gate insulating layer comprising high-K dielectric materialmay be adopted in conjunction with a metal gate material, whichgenerally offers superior electrical performance over conventionalpolysilicon materials.

In some embodiments, the insulating layer 103 may comprise a multi-layerstructure. Depending on application and operational requirements, themulti-layer insulating layer may comprise sub-layers of differentdielectric materials and distinct thicknesses. Additional dielectricsub-layers in the gate insulator may enable the tuning of structuralinterface property, such as reducing interface damage between differentmaterial layers or providing additional structural protection. Forinstance, in some embodiments, the insulating layer 103 comprises afirst dielectric sub-layer disposed over the gate insulator andcomprises substantially of silicon nitride (SiNx) material, and a seconddielectric sub-layer disposed over the first dielectric sub-layer andmade substantially of silicon oxide (SiOx). The coverage of gatedielectric layer over the channel layer 104 is of particular importancefor preventing potential shorting between gate and the source/drainregions in the TFT device 100.

The channel layer 104 defines the semiconductive/active region of theTFT device 100 through which charge carriers may traverse. As the gatestructure (e.g., defined by the first conductive layer 102) is formedvertically under the channel layer 104, such a device architecture maybe referred to as the “bottom gate” arrangement. The channel layer 104may comprise a suitable semiconducting material, which may selectivelyinclude an oxide semiconductor, elemental semiconductor, compoundsemiconductor, and alloy semiconductor material. The semiconductivematerial may be selectively disposed in one of an amorphous,crystalline, and poly-crystalline state, or a combination of the states.In some embodiments, the channel layer 104 comprises one or more oxidetype compound semiconduction material, such as indium-gallium-zinc oxide(IGZO), indium-zinc-tin oxide (IZTO), indium-gallium-tin oxide (IGTO),and indium-aluminum-zinc oxide (IAZO) material. In some embodiments, thechannel layer 104 comprises substantially hydrogenated amorphous silicon(a-Si:H). The amorphous silicon channel material, Which offers decentcharge carrier mobility (e.g., about 0.1-1 cm̂²v̂⁻¹ŝ⁻¹) and high thin filmUniformity, may be implemented economically for large scale fabrication.In some embodiments, the channel layer 104 comprises polycrystallinesilicon material prepared in a low temperature process (e.g., lowtemperature polycrystalline silicone, LTPS). The LTPS channel materialoffers superior charge carrier mobility (e.g., about 100-200 cm̂²v̂⁻¹ŝ⁻¹),but requires higher fabrication cost, particularly in the application oflarge size display panel devices.

In some embodiments, the channel layer 104 comprises an oxidesemiconducting material that includes one or more of, e.g., zinc (Zn),indium (In), tin (Sn), gallium (Ga), hafnium (H). In the presentexemplary embodiment, the channel layer 104 comprisesindium-gallium-zinc based oxide material (e.g., IGZO). There is noparticular limitation on the ratio of the components of thesemiconducting oxide material, and additional component may be presentin the oxide. The IGZO channel material possesses both high filmuniformity and carrier mobility tunable through the ratio between itscompound components to achieve carrier mobility greater than 10cm²v⁻¹s⁻¹ and low leakage current), which makes it suitable for largearea applications.

The high carrier mobility property and low leakage characteristics ofthe IGZO material may enable further minimization of the device featuresin a display array panel to achieve increased display resolution.

The second conductive layer (e.g., patterned to define the source/drainelectrode 105 a/b of the TFT device 100, which may be collectivelyreferred to as conductive layer 105) is disposed over the channel layer104. For instance, selective portion of the conductive layer 105 may bearranged over the channel layer 104 and in electrical contactthere-with. The conductive layer 105 may be arranged to form an array ofsecond level signal conducting lines. As shown in FIG. 1, the conductivelayer 105 may be part of the signal conducting network thatinterconnects an array of pixel elements. For example, the secondconductive layer 104 may be patterned to form a second level signalconducting array/network over the substrate 101 (e.g., data lines 112 asshown in FIG. 1), with portions thereof traversing horizontally betweenone region (e.g., the source drain region of a TFT device 100) andanother region (e.g, a data line driving IC) defined over the substrate.Moreover portions of the conductive layer 105 may be patterned to definethe source and drain electrodes of the TFT devices 100 (e.g., thesource/drain terminals as shown in FIG. 1). The integrally formed signalconducting line (e.g., the data lines) and the TFT device terminal(e.g., the source/drain electrodes 105 a/b) may reduce device structuralcomplexity (and thus fabrication complexity and cost).

As shown in FIG. 2, the conductive layer 105 is patterned to form theelectrically separated source and drain terminals (e.g., source/drainelectrodes 105 a, 105 b) above the gate region (e.g., over the gateelectrode 102) of the TFT device 100. The patterning of the conductivelayer 105 may be carried out by a suitable etching process (e.g., wetetching) that generates a gap 106 therein that electrically separatesone portion of the layer 105 from the other, thus defining a sourceregion (e.g., electrode 105 a) and a drain region (e.g., electrode 105b) of the TFT device 100 (of course, the source and the drain of atransistor device is interchangeable). Particularly, FIG. 2 illustratesa generally regular and tapered gap profile between the source and thedraw electrodes 105 a, 105 b. As will be further discussed, asubstantially smooth and tapered profile is generally desirable forachieving higher structural integrity and better electrical propertiesin the TFT device 100.

At least a portion of the conductive layer 105 may comprise amulti-layered structure (e.g., the instant example illustrates atri-layer structure). For example, at the source/drain region of the TFTdevice 100, the conductive layer 105 comprises a multi-layered structurethat includes a first (e.g., lower) sub-layer 105-1 arranged inelectrical contact with the channel layer 104, a second (e.g., middle)sub-layer 105-2 disposed over the first sub-layer 105-1, and a third(e.g., upper) sub-layer 105-3 disposed over the second sub-layer 105-2.However, in some embodiments, a multi-layered arrangement need not beapplied throughout the entire conductive layer 105. For instance,certain regions in the second conductive lavers 105 may be arranged tocomprise a structure of a double or even a single sub-laver layout,depending on particular device requirements and/or other operationaldesign needs.

The upper and the lower sub-layers 105-1/105-3 may be substantially madeof a compound conductor that comprises more than one types of chemicalelements formulated at particular content ratios. In some embodiments,the first sub layer 105-1 (which may be referred to as the bottombarrier layer, i.e., BBL) comprises substantially a transparentconductive oxide (TCO) material. Examples of transparent conductiveoxide may include indium-tin oxide (ITO), indium-zinc Oxide (IZO),gallium-zinc oxide (GZO), aluminum-zinc oxide (AZO), and suitablecombinations thereof. The second sub-layer 105-2 (which may be referredto as the middle conductive layer, i.e., MCL) may be substantially madeof an effective conducting material. For instance, the second sub-layercomprises at least one of a metal and a metal alloy material. In someembodiments, the second sub-layer comprises at least one of an aluminum(Al), copper (Cu), manganese (Mn), molybdenum (Mo), and molybdenumtungsten (MON) material. The third sub-layer 105-3 (which may bereferred to as the top capping layer, i.e., TCL) may be made of amaterial comparable to that used in the first sub-layer 105-1, but maybe provided with different component composition ratios.

In some embodiments, the abovementioned multi-layered conductingstructure may also be implemented in the first level signal conductingarray (e.g., to define the gate lines and/or gate electrodes).Nevertheless, the choice of materials and the content composition ratiosused in a first level conducting layer (e.g., the gate lines 112) neednot be the same as that adopted in the second level conducting layer(e.g,, the data lines 111 and the S/D electrodes), and may be selectedbased on specific design requirements or other practical concerns. Inaddition, the multi-layered conducting structure in accordance with theinstant disclosure may be adopted not only in a “bottom gate” device(such as illustrated in FIG. 2) but also applicable in “top gate”applications.

The provision of the upper and the lower sub-layers 105-1/105-3 mayincrease adhesiveness between the MCL, with the rest of the devicestructures, thereby enhancing the level of structural integrity in theTFT device 100. Moreover, the upper and the lower sub-layers 105-1/105-3may comprise suitable materials that function as diffusion barrierlayers to allow the implementation of materials having high conductivityyet with active self diffusing properties. For example, copper (Cu)metal (or an alloy thereof) possesses low electricalresistance/impedance, hose superior electrical properties make itsuitable for high conductivity applications. However, copper is also anactive material that tends to self-diffuse/migrate within a devicestructure during fabrication process. The diffusion of copper atoms tocertain locations (e.g., the channel region) in a device may causedegradation of device performance (i.e., copper contamination). Theupper and the lower sub-layers 105-1/105-3 may be implemented to serveas diffusion harrier layers to confine the cupper atoms within thedesirable regions in an electronic device, thereby enhancing the signalconducting quality of the device while maintaining device reliability.Moreover, the lower sub-layer 105-1 may provide an Ohmic contactbuffering interface between the MCL (e.g., in this case, comprisedsubstantially of copper material) and the channel layer (e.g, in thiscase, comprised substantially of IGZO material). The material in thefirst and the second sub-layers 105-1/105-3 of the conductive layer 105may be selected based on its etching properties, e.g., the etch rate andselectivity. For instance, a conductive oxide material having comparableetch rate with the MCL (e.g., sub-layer 105-2) may be adopted in theupper and the lower sub-layers 105-1/105-3. For example, when the middlesub-layer 105-2 is substantially made of copper, the upper and the lowersub-layers 105-1, 105-3 may comprise substantially ITO or IZO. Mindfulselection of the material for the multi-layered conductive structure(e.g., layer 105) may enable significant reduction of fabrication costs.By way of example, wet-etching friendly materials (one example beingIZO) may be selected to alleviate the reliance on expensive fabricationequipment (e.g., dry etching device) and/or time inefficient processingprocedures.

In some embodiments, the channel layer 104 is provided with an averagethickness in the range of about 200 to 350 A (angstrom). In someembodiments, the first sub-layer (BBL 105-1) comprises an averagethickness in the range of about 200 to 300 A. In some embodiments, thesecond sub-layer (MCL 105-2) comprises an average thickness in the rangeof about 2000 to 3500 A. In some embodiments, the third sub-layer (TCL105-3) comprises an average thickness of about 200 to 350 A.Nevertheless, the actual layer thickness may be dependent on applicationrequirements and/or other practical concerns.

FIGS. 3A-3B illustrate different etch profiles in the multi-layeredconductive layer 105 undergone a patterning process (e.g., correspondsto the regional enlargement view of the circled portion shown in FIG.2). Particularly, FIGS. 3A-3D illustrate that different compositionratios of the material component in the upper and the lower sub-layersTCL 105-3 and the BBL 105-1) affect different lateral etch profiles inthe conductive layer 105. The content ratio of the element components inthe different sub-layers of the conductive layer 105 may affect alateral etch profile therein. Accordingly, the tuning of the componentcontent ratios in the upper and the lower sub-layers 105-1, 105-3 (e.g.,the content ratio differentiation there-between) may play an essentialrole in the generation of a desirable lateral etch profile in the TFTdevice (e.g., device 100).

FIG. 3A illustrates a first lateral etch profile in the conductive layer105 in a first scenario (under a first sub-layer content ratioarrangement). The etch profile shown in FIG. 3A corresponds to asubstantially uniformly slopped, obliquely inclining lateral etchsurface, which may provide beneficial structural and electricalcharacteristics in a TFT device in most applications. In the embodimentshown in FIG. 3A, each of the first and the third sub-layers comprises ametal oxide material containing indium (In) and zinc (Zn). In someinstances, the etch rate of the indium (In) component in the conductivelayer 105 is noticeably slower than that of the zinc (Zn) component withrespect to the etchant employed during the patterning process. Whileindium (In) generally offers superior elecnical conductivity, a delicatebalance between the content ratio of indium (In) and zinc (Zn) may berequired to strike a practical compromise betvveen the electricalconductive characteristics of the sub-layers and the process-abilitythereof.

In the instant embodiment, the indium to zinc content ratio (i.e., theratio of the indium content to the zinc content, which may be calculatedby atomic content ratio or other suitable measures) in the firstsub-layer 105-1 is greater than an indium to zinc content ratio in thethird sub-layer 105-3 (the content ratio of the substances in the thinfilm layers may be determined by, for instance, the energy dispersivespectrometer, EDS), Such an indium to zinc content ratio differentiationbetween the capping and the bottom sub-layers 105-3/105-1 helps to shapea lateral etch profile associated with the gap generated in theconductive layer 105 between the source and the drain electrodes, wherethe gap width associated there-with in the third sub-layer is wider thanthat that in the first sub-layer.

FIG. 3B illustrates a second lateral etch profile in the conductivelayer 105 in another scenario (under a different sub-layer content ratioformulation). The etch profile shown in FIG. 3B corresponds to anunder-etching situation in the capping sub-layer 105-3, resulting in thegeneration of an overhang structure in the etched portion of theconductive layer 105. In the instant example, the over-hang featureprimarily occurs in the upper sub-layer 105-3. This may be a result ofexcessive indium content in the upper sub-layer 105-3, thus causing anoverly slow etch rate in the top capping layer. An over-hang feature maybe undesirable, as such a structural geometry tend to weaken the overallstructural integrity of a semiconductor device (e.g., TFT device 100).By way of example, the overhang feature in the TCL 105-3 of theconductive layer 105 inevitably shadows certain regions proximate theunderlying sub-layers (e.g., MCL 105-2 and/or BBL 105-1), thuspotentially hinders the depositionifonnation) of subsequent devicefeatures. For instance, voids may be generated in the TFT deviceproximate the sub-layer interface region between the TCL and the MCL/BBLas a result of the overhang feature. Voids in the TFT device mayadversely atTect the structural integrity. For example, the uppersub-layer 105-3 (and other device features subsequently formed thereon)may be physically severed (e.g., peeled off) from the lower layers(especially in a flexible panel device application). Also, voids in theconductive structure (e.g., the second level metal layer, such as theconductive layer 105) may alter the electrical property of the device(e.g., parasitic capacitance characteristics).

FIG. 3C illustrates a third lateral etch profile in the conductive layer105 in another scenario (under a different sub-layer content ratioformulation). The etch profile shown in FIG. 3C corresponds to anunder-etch situation in the lower sub-layer 105-1, in which a bottomresidual tail feature is left in the conductive layer 105. This may be aresult of excessive indium content in the lower sub-layer 105-1, thuscausing a overly slow etch rate in the bottom barrier layer. In the TFTdevice, a long residual tail feature in the second level conductinglayer (e.g., layer 105) proximate the channel region (e.g., the regionabove the channel layer 104) may affect the channel length of the TFTdevice. For instance, the residual tail in the BBL 105-1 may result in areduction of effective device channel length, thereby impacting theelectrical performance of the TFT device. Also, the bottom residualfeature mays result in an over shallow slop in the lateral etch profileat the channel region (e.g., between the source and the drain electrodes105 a/105 b), which may result in higher parasitic capacitance.

FIG. 3D illustrates a fourth lateral etch profile in the conductivelayer 105 in yet another scenario (under a different sub-layer contentratio arrangement). The etch profile shown in FIG. 3D corresponds to anover-etching situation in the bottom sub-layer 105-3, resulting in thegeneration of an undercut structure in the etched portion of theconductive layer 105. In the instant example, the undercut featureprimarily manifests in the bottom sub-layer region. This may be a resultof excessive zinc content in the lower sub-layer 105-1 as well asinsufficient indium to zinc content ratio differentiation between theTCL 105-3 and the BBL 105-1. As previously discussed, an undercutfeature may be undesirable from a structural integrity perspective, assuch a condition may weaken the overall structural integrity of asemiconductor device (e.g., TFT device 100). By way of example, voidsmay be generated in the TFT device proximate (or underneath) an undercutfeature, which may adversely affect the structural and electricalproperties of the TFT device. As a result, the upper sub-layers (e.g.,the MCL 105-2, the TCL 105-3, and other device features subsequentlyformed thereon) play be more prone to physical damage (e.g., severancefrom the lower layers), especially in a flexible panel deviceapplication.

Please refer back to FIG. 3A. Attentions in certain process conditionsmay be required during the fabrication of a semiconductor device (e.g.,device 100) to generate the structural profile as shown in FIG. 3A.Among them, it is found that the indium to zinc content ratiodifferentiation may be kept sufficiently large to ensure the generationof a substantially regularly slopped lateral etch profile (asillustrated in FIGS. 2 and 3A). Referring back to FIG. 2, the pair ofopposing lateral surfaces formed in the conductive layer 105 (betweenwhich the gap 106 is defined) cooperatively shape a substantiallytapered gap profile between the source and the drain electrodes 105 a,105 b, where a gap width associated with the upper sub-layer (e.g.,layer 105-3) is wider than that associated with the lower sub-layer(e.g., layer 105-1).

As discussed previously, the indium to zinc content ratio in the firstsub-layer 105-1 is greater than that in the third sub-layer 105-3. Toprovide further examples, the indium and the zinc contents in the lowersub-layer 105-1 may substantially define a first indium to zinc ratio(i.e., In_((BBL)):Zn_((BBL))=R₁, which is a ratio expressible in %).Likewise, the indium and the zinc contents in the upper sub-layer 105-3substantially define a second indium to zinc ratio (i.e.,In_((TCL)):Zn_((TCL))=R₂, expressible in %). In the instant embodiment,the multi-layered conductive layer 105 is provided with a first contentratio R₁ greater than the second content ratio R₂ to achieve a lateraletch profile comparable to that shown in FIGS. 2 and 3 a (in otherwords, R₁>R₂).

For instance, in one embodiment, the indium content in the uppersub-layer 105-3 is about 0.15 units, and the zinc content is about 0.85units. Accordingly, the indium to zinc content ratio in the uppersub-layer 105-3 (i.e., R₂=In_((TCL)):Zn_((TCL))=0.15/0.85) is about17.6%. On the other hand, the indium content and the zinc content in thelower sub-layer 105-1 is about 0.35 and 0.65, respectively. Accordingly,the indium to zinc content ratio in the lower sub-layer 105-1 (i.e.,R₁=In_((BBL)):Zn_((BBL))=0.35/0.65) is about 53.8%. The content ratiocondition in the sub-layers (where R₁>R₂) may thus yield a substantiallydownward tapered etch profile in the conductive layer 105 comparable tothat illustrated in. FIG. 2.

The difference of the content ratios between the lower and the uppersub-layers may be larger than a threshold value to preserve favorableprocess conditions that leads to a desirable lateral etch profile. It isfound that an indium to zinc content ratio difference of greater than orequal to 20% bete een the first and the third sub-layers 105-1, 105-3would yield a lateral etch profile in the conductive layer 105 withfavorable characteristics. Take the previous embodiment as example, theindium to zinc content ratio difference between the lower sub-layer105-1 and that of the upper sub-layer 105-3 is about 36%(R1−R2=53.8%−17.6%), which satisfies the abovementioned condition. Asufficient content ratio difference that meets the minimum thresholdcondition may help to prevent the formation of an undesirable undercutfeature, such as that illustrated in FIG. 3D.

As further examples, in some embodiments, the indium to zinc contentratio in the lower sub-layer 105-1 ranges from about 25% to about 80%.In further embodiments, the indium to zinc content ratio in the lowersub-layer 1054 ranges from about 45% to about 70%. On the other hand, insome embodiments, the indium to zinc atomic ratio in the upper sUb-layer105-3 ranges from about 5% to about 40%. In further embodiments, theindium to zinc atomic ratio in the upper sub-layer 105-3 ranges fromabout 10% to about 35%. In accordance with embodiments of the instantdisclosure, the tuning of the indium to zinc content ratiodifferentiation between the lower and the upper sub-layers 105-1, 105-3affects the generation of a substantially smooth and tapered lateralprofile for the gap defined between the source and the drain electrodes105 a/105 b (e.g., gap 106). Moreover, in some embodiments, the lateralprofile associated with the etched gap defined in the conductive layer105 corresponds to a taper angle of about 40 degrees to 85 degrees withrespect to a surface defined by the channel layer. It is noted that, anobtuse taper angle in the lateral etch profile of the conductive layer(e.g., layer 105) creates an overhang/undercut feature that may causeissues in subsequent device feature integration, as discussedpreviously. On the other hand, an overly acute taper angle in thelateral etch profile of the conductive layer may consume extra planarbudget in a high feature density device and adversely impact the channellength of the device. Moreover, an overly shallow taper angle may inducehigher parasitic capacitance around the corresponding regions. In someembodiments, a taper angle of about 60 to about 70 degrees in thelateral etch profile of the conductive layer (e.g., layer 105) isachieved through proper process condition. tuning to ensure devicereliability.

FIG. 4 shows a cross sectional view of a ITT device in an exemplaryarray panel in accordance with some embodiments of the instantdisclosure. Particularly, FIG. 4 shows a cross sectional view of anexemplary TFT device 100′ across both the source and the drain terminals(e.g., S/D electrodes 105 a′, 105 b′). As shown in FIG. 4, in someembodiments, the conductive layer 105 may be provided with one or moreadditional sub-layers. For example, in the instant exemplary embodiment,the conductive layer 105 is further provided with an additionalsub-layer 105-4 disposed between the first sub-layer 105-1 and thesecond sub-layer 105-2. The additional sub-layer 105-4 may also becomprised of a metal oxide layer containing indium and zinc, wherein anindium to zinc content ratio in the additional sub-layer 105-4 isgreater than an indium to zinc content ratio in the third sub-layer105-3 (yet smaller than that in the first sub-layer 105-1). With theinsertion of additional sub-layers in the BBL, the etchingcharacteristics in the second level conductive layer (e.g., layer 105)may be preserved, while higher indium content may be employed in theBottom-most sub-layer (e.g., sub-layer 105-1) of the BBL to furtherimprove the electrical properties at the contact interface between theconductive layer 105 and the channel layer 104 (e.g., for Ohm contactreduction). Accordingly, in some embodiments, the indium content in thefirst sub-layer 105-1 is greater than that in the additional sub-layer105-4. In some embodiments, the indium content ratio between the indiumcontent in the first sub-layer 105-1 and that in the additionalsub-laver 105-4 is in a range of more than 1 to about 1.5. In furtherembodiments where more than one additional sub-layers are provided inthe BBL, the indium content (or, in some cases, the indium to zinccontent ratio) in one of the additional sub-layers closer to the firstlayer 105-1 should be higher than that in the one further awaythere-from, for similar reasons as previously discussed.

Please refer to FIGS. -5A-5B, which illustrate an exemplarysemiconductor device (e.g., TFT device 100) in accordance with someembodiments of the instant disclosure at various stages of fabricationprocess.

FIG. 5A provides an exemplary regional cross sectional view illustratingthe deposition of a first conductive layer (e.g., layer 102) over amajor surface of a substrate (e.g., substrate 101). The substrate maycomprise an insulating material. In some applications, suitablematerials for the substrate may include glass, quartz, and plastichaving sufficient optical transparency (e.g., for electromagneticradiations in the visible spectrum for visual display applications). Insome applications, the substrate may comprise ceramic and/or siliconmaterials. In some applications, flexible substrate materials may beadopted. Suitable choice of material for flexible substrate may include,for example, polyethersullone (PES), polyethylenenaphthalate (PEN),polyethylene (PE), polyimide (PI), polyvinyl chloride (PVC),polyethylene terephthalate (PET), and stainless steel, or combinationsthereof.

The first conductive layer may be disposed over the substrate usingsuitable deposition techniques, including physical thin film depositionmethods such as sputtering (e.g., PVD, PEPVD). The first levelconducting layer may then be patterned using suitable etching techniquesto define an array of first level signal conducting lines (e.g., gatelines 111 as shown in FIG. 1). For instance, the first conductive layermay be patterned to establish electricallsignal connection between afirst region (e.g the gate region of the TFT device) to a second region(e.g., a date line driving IC) defined over the major surface of thesubstrate, in some applications, portions of the first conductive layermay be patterned to define the gate electrodes of the TFT devices. Theintegrated signal conducting line (e.g., the gate lines) and the TFTdevice terminal (e.g., the gate electrode 102) may reduce devicestructural complexity and thus fabrication complexity.

The first conductive layer may selectively comprise aluminum (Al),silver (Ag), gold (Au), cobalt (Co), chromium (Cr), copper (Cu), indium(In), manganese (Mn), molybdenum (Mo), nickel (Ni), neodymium (Nd),palladium (pd), platinum (Pt), titanium (Ti), tungsten (W), zinc (Zn),other suitable conductive materials, and a suitable mixture/alloythereof. For achieving higher optical efficiency, in some embodiments,the first conductive layer may include a transparent conductivematerial, such as indium tin oxide (ITO), indium zinc oxide (IZO),aluminum doped zinc oxide (AZO), or a suitable combination thereof

FIG. 5B provides an exemplary regional cross sectional view illustratingthe deposition of a gate insulating layer (e.g., layer 103) over thefirst conductive layer. The gate insulating layer may be disposed viaone or more suitable thin film deposition technique (which may includephysical andfor chemical thin film deposition methods) to form aprotective layer that prevents die conductive gate line structures(e.g., layer 102) from shorting with the subsequently formed devicefeatures. The insulating layer may be made of one or more suitabledielectric material, such as silicon oxide (SiOx) silicon nitride (SiNx)silicon oxynitride (SiOxNy), aluminum oxide (AlOx), yttrium oxide(Y2O3), hathium oxide (HfOx), zirconium oxide (ZrOx) aluminum nitride(AlN), aluminum oxynitride (AlNO), titanium oxide (TiOx), bariumtitanate (BaTiO3), lead titanate (PbTiO3). In some applications, one ormore high-K dielectric material may be used as gate insulator for theTFT device (e.g., device 100), The high-K dielectric material mayinclude, for example, oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf, Al,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixturesthereof. A gate insulating layer comprising high-K dielectric, materialmay be adopted in conjunction with a metal gate material, which mayoffer superior electrical performance over conventional polysiliconmaterials. In some applications, the insulating layer 103 may beprovided with a multi-layer structural configuration.

FIG. 5C provides an exemplary regional cross sectional view illustratingthe deposition of a channel material layer (e.g., layer 104). Thechannel material layer may be disposed over the gate insulating layer(e.g., layer 103) using suitable deposition techniques, includingphysical thin film deposition methods such as sputtering (e.g., PVD,PEPVD). The channel layer may comprise a suitable semiconductingmaterial, selected from at least one of an oxide semiconductor,elemental semiconductor, compound semiconductor, and alloy semiconductormaterial. The semiconductive material may be selectively disposed in oneof an amorphous, crystalline, and poly-crystalline state, or acombination of the states. In some applications, one or more oxide typecompound semiconducting material, such as indium-gallium-zinc oxide(IGZO), indium-zinc-tin oxide (IZTO), oxide (IGTO), andindium-aluminum-zinc oxide (IAZO) material, is used in the channelmaterial layer.

The channel layer may then be patterned to define thesemiconductivelactive region of the TFT device (e.g., device 100)through which charge carriers may traverse. Depending on the choice ofchannel material, the channel layer may be patterned at this stage usinga standalone etching process (which may correspond to a first etch mask,as illustrated in the instant figure). In such a case, the subsequentlydisposed second level conductive layer (e.g., layer 105 as shown in FIG.5F) may be separately patterned using a second etching process (whichmay correspond to a second etch mask). However, in some embodiments, thematerials for the channel layer and the second conductive layer arechosen with comparable etching characteristics. The materialcompatibility between the channel layer and the subsequently disposedsecond conductive layer may enable a concurrent etching process forpatterning both layers using a single etch mask. The reduction in etchmask requirement may significantly lower the process complexity and thefabrication cost. By way of example, in some embodiments, thesemiconductive IGZO material and the transparent IZO material areselected as the channel material and the second conductive layermaterial, respectively, to take advantage of their comparable etchingcharacteristics.

FIG. 5D provides a regional cross sectional view illustrating an initialdeposition stage of a multi-layered second conductive structure (e.g.,the deposition of the lower sub-layer of the conductive layer 105). Inthe instant exemplary process, a first (lower) sub-layer (e.g., BBL105-1) is disposed over the channel layer (e.g., layer 104) via suitabledeposition techniques, such as sputtering (e.g., PVD, PEPVD). In someapplications, the BBL substantially comprises one or more transparentconductive oxide (TCO) material, such as indium-tin oxide (ITO),iridium-zinc oxide (IZO), gallium-zinc oxide (GZO), aluminum-zinc oxide(AZO) or a suitable combination thereof. The BBL may provide an Ohmiccontact buffering interface between the channel layer of IGZO material)and the subsequently disposed conductive layers (e.g., of Cu material),which may improve the electrical properties at the sub-layer interface(e.g., interface resistance reduction).

FIG. 5D also illustrates an optional treatment for BBL 105-1. Aspreviously discussed, the conductive layer 105 may comprise amultilayered portion, in which a middle conductive layer (MCL) isdisposed Met the BBL 105-1 (e.g., layer 105-2 as shown in FIG. 5E).While both the lower and the middle sub-layers are made of substantiallyconductive materials, the electrical properties thereof may differ. Forinstance, in the instant example, the lower sub-layer is substantiallymade of a TCO material (e.g., IZO), while the middle sub-layer is madeprimarily of a metallic substance (e.g., Cu). To further improve theelectrical characteristics at the material interface between the lowerand the middle sub-layers, an optional treatment may be implemented tointroduce additional hydrogen (H) content into the lower sub-layer (BBL)before the deposition of the middle sub-layer (MCL). The introduction ofadditional hydrogen content may be done by ammonia plasia a treatment,hydrogen annealing process, and/or other suitable methods.

It has been measured that (e.g., using a four point probe resistivitymeasurement), compared to a barrier sub-layer that does not receive anoptional treatment (whose hydrogen content concentration is typically inthe order of 10^(̂21) cm^(̂−3)), a treated lower sub-layer may boost a 20%increase in hydrogen content or more. The increased hydrogen content inthe lower sub-layer corresponds to a higher carrier concentration in thethin film structure, therefore helps to improve the electricalproperties at the interface region between the hetero-materialsub-layers (e.g., further reduced contact resistance). In someembodiments, a BBL that receives a hydrogen treatment may reflect anincrease in electrical conductivity of 10% or more.

As previously discussed, sensible selection of the, material(s) for themulti-layered conductive structure (e.g., layer 105) may also contributeto the reduction of fabrication costs. By way of example, wet-etchingfriendly materials (e.g., IZO/Cu/IZO) may be selected to alleviate thereliance on expensive fabrication equipment (e.g., dry etchingequipment) and/or associated time consuming processing procedures.

FIG. 5E provides a regional cross sectional view illustrating thedeposition of the remaining sub-layers (e.g., layers 105-2, 105-3) ofthe second conductive layer. The instant figure also shows an optionalsecond treatment for the upper sub-layer layer 105-3) thereof. In theillustrated process, a second (middle) sub-layer 105-2 and a third(upper) sub-layer 105-3 are respectively and successively disposed overthe lower sub-layer (layer 105-1). Each of the middle sub-layer (MCL)and the upper sub-layer (ICL) may be formed using suitable depositiontechnique(s), such as sputtering (e.g, PVD, PEPVD). The second sub-layermay be substantially made of a material having good electricalconductivity, such as a metal or a metal alloy. In some applications,the second sub-layer comprises at least one of an aluminum (Al), copper(Cu), manganese (Mn), molybdenum (Mo), and molybdenum tungsten (MoW)material. On the other hand, in some applications, the third sub-layercomprises substantially a transparent conductive oxide (TCO) material,such as indium-tin oxide (ITO), indium-zinc oxide (IZO), gallium-zincoxide (GZO), aluminum-zinc oxide (AZO), and suitable combinationsthereof. The third sub-layer may be made of a material comparable tothat used in the first sub-layer, but provided with a differentcomponent composition ratio.

Further conductive features (e.g., conductive lines/vias) may bearranged over the upper sub-layer (TCL) and electrically connectedthereto not shown in instant figures) for establishing signal conductionpaths from/to the exemplary semiconductor device (e.g., device 100).Therefore, to further improve the electrical characteristics at thematerial interface between the upper sub-layers and the subsequentconductive features, a second optional treatment may be implemented tointroduce additional hydrogen (H) content into the upper sub-layer (TCL)in a similar fashion. As discussed above, compared to a cappingsub-layer that does not receive an optional treatment (whose hydrogencontent concentration is typically in the order of 10^(̂21) cm^(̂−3)), atreated lower sub-layer may boost a 20% increase in hydrogen content ormore. The increased hydrogen content in the lower sub-layer correspondsto a higher carrier concentration in the thin film structure, thereforehelps to improve the electrical properties at the interface regionbetween the hetero-material sub-layers (eg, further reducing contactresistance). In some embodiments, a TCL that receives a hydrogentreatment may reflect an increase in electrical conductivity of 10% ormore.

FIG. 5F provides a regional cross sectional view illustrating apatterning of the second conductive layer fbr defining a source and adrain electrode of the exemplary semiconductor device. In the instantexemplary process, the second conductive layer (e.g., layer 105) ispatterned to form the elecnically separated source and drain terminals(e.g,, source/drain electrodes 105 a, 105 b) above the gate region(e.g., over the gate electrode 102) of the device. The patterning of thesecond conductive layer may be carried out by a suitable etching process(e.g., wet etching) that generates a gap (e.g., recess feature 106)therein that electrically separates the one portion of the secondconductive layer from the other, thereby defining a source region and adrain region of the device. As discussed previously, the content ratioof the element components in the different sub-layers of the secondconductive layer may affect a lateral etch profile associated with therecess feature 106. B way of example, the tuning of the componentcontent ratios in the upper and the lower sub-layers 105-1, 105-3 (e.g.,the content ratio differentiation there-between) may play an essentialrole in the generation of a desirable lateral etch profile in the TFTdevice.

In the instant exemplary process, each of the first and the thirdsub-layers are provided with a metal oxide material containing indium(In) and zinc (Zn). Moreover, the indium to zinc content ratio in thefirst sub-layer is greater than an indium to zinc content ratio in thethird sub-layer. As previously discussed, such an indium to zinc contentratio differentiation between the capping and the bottom sub-layershelps to shape a lateral etch profile associated with the gap generatedin the second conductive layer. In addition, the indium to zinc contentratio differentiation is kept above a certain threshold value to ensurethe generation of a suitable lateral etch profile. In the instantexample, an indium to zinc content ratio difference of greater than orequal to 20% is provided between the first and the third sub-layers tohelp shaping a proper lateral etch profile in the second conductivelayer. In some embodiments, the lateral profile associated with theetched gap defined in the second conductive layer corresponds to a taperangle ranged from about 40 degrees to 85 degrees with respect to asurface defined by the channel layer.

The schematic illustration of FIG. 5F shows a smooth and downwardlytapered etch profile between the source and the drain regions 105 a, 105b, which possesses a wider separation width at the top (e.g., at the TCPregion) and a narrower width at the bottom (e.g., at the BBL region). Itis noted that, subject to different zooms of magnification, it ispractically rare to find a precisely/univenally linear lateral etchedsurface (e.g., a straight lateral profile that defines a fixed constantslope). Nevertheless, as previously discussed, proper tuning of thematerial content ratios in the second conductive layer may enable thegeneration of a substantially uniformly slopped, obliquely inclininglateral etch surfaces in the second conductive layer (for instance,maintaining a substantially continuously inclining lateral slope withoutobviously observable profile interruption, e.g., overhang and/orundercut).

Likewise, a precise definition of a fixed taper angle in the lateraletch profile may not be easy in a practical situation. However, as arealistic approach for the determination of the taper angle insituations where die slope of the lateral etched surface issubstantially regular and non-interrupted (e.g., no substantialformation of overhang and/or undercut), the taper angle associated withthe lateral etch profile may be taken as an average value, e.g., takenas the angle defined between the major surface of the substrate and aline defined between the lower corner of the inclined etched profile inthe MCL (e.g., layer 105-2) and the uptier corner thereof (e.g.,substantially corresponds to the lower point and the upper point of theMCL). Nevertheless, in some situations, a local approach for thedetermination of a corresponding taper angle may apply.

As previously mentioned, in some embodiments, the second conductivelayer may be provided with one or more additional sub-layers. Forexample, an additional sub-layer (not shown) may be disposed between thefirst sub-layer (BBL) 105-1 and the second sub-layer (MCL) 105-2. Theadditional sub-layer may also comprise a metal oxide material containingindium and zinc, Wherein an indium to zinc content ratio in theadditional sub-layer is greater than an indium to zinc content ratio inthe third sub-layer (TCL) 105-3 (yet smaller than that in the firstsub-layer 105-1), The insertion of additional sub-layer(s) may preservethe etching characteristics in the second loiel conductive layer whileallowing higher indium content to be employed (e.g., at the bottom-mostsub-layer of the BBL), thereby further improving the electricalproperties at the contact interface between the conductive layer 105 andthe channel layer 104 (e.g., for Ohmic contact reduction). In theapplications where more than one additional sub-layers are provided inthe BBL, the indium content in one of the additional sub-layers closerto the first layer 105-1 may be higher than that in the one further awaythere-from.

FIG. 5G prosides a regional cross sectional VieW illustrating thedeposition of subsequent passivation layer(s) over the source/drainstructure of the exemplary semiconductor device (e.g., TFT device 100).For example, one or more passiyation layer(s) (e.g., layer 107) may bedisposed over the exposed top surface of the second conductive layer(e.g., layer 105), the exposed surface of the lateral etch profilethereof, and the exposed region of the channel material layer (e.g.,layer 104). The passivation layer(s) may provide protection for the TFTdevice from damage during the subsequent fabrication processes.Moreover, certain channel materials (e.g., IGZO) are sensitive toambient conditions (e.g., oxygen and moisture/water). The passivationlayer(s) of suitable dielectric materials(s) (e.g., siliconoxide/nitride) of sufficient thickness over the TFT device 100 may helpto protect the delicate device structures from potential environmentalhazards. In some embodiments, the passivation layer may be conformallydisposed over the exposed surfaces of the TFT device usinp, one or moresuitable deposition technique(s) (e.g., chemical deposition methods suchas CVD/PECVD/MOCVD). With the passivation layer(s) in place, thesemiconductor device may subsequently undergo an annealing process forchannel activation.

In some scenarios, a lateral byproduct layer as illustrated in FIGS.6a-c and FIGS. 8a-b ) may be formed at certain exposed region(s) of thesemiconductor device (e.g., TFT device 100) during the deposition of thepassivation layer(s). By way of example, the passivation layer ofsilicon oxide material) may be disposed using the PECVD process, whichis an energy-enhanced thin film deposition method that otters highefficiency in mass production applications. However, during thedeposition process, high energy plasma may cause chemical reaction atcertain exposed region of the semiconductor device, resulting in theformation of a by-product layer. For instance, in certain embodimentswhere the highly conductively (and chemically active) copper material isused in the MCL of the second conductive layer (e.g., layer 105-2), thehigh energy plasma during the passivation process may cause theformation of a copper oxide (CuO) byproduct layer over the exposedcopper material surface at the lateral etch profile region. In certaininstances, the formation of a lateral byproduct layer (e.g., a lateralCuO layer) may be inevitable, and intentional removal of such layer mayincrease process complexity and incur additional costs.

FIGS. 6A-6C are microscopic cross sectional pictures showing the lateraletch profiles in various exemplary second conductive layers.

FIG. 6A provides a SEM (scanning electron microscopy) picture showing alateral etched region in one exemplary multi-layered conductingstructure (e.g., layer 105). Particularly, the microscopic enlargementview shows a lateral surface region of the MCL material in themulti-layered structure converted into an irregular, fuzzy-lookingbyproduct layer (which may be referred to as the lateral byproductlayer, i.e., LBL) having significant surface undulation with littlelayer thickness uniformity. Moreover, it can be observed that the lowerportion of the byproduct layer proximate the channel layer has anoticeably larger thickness, and extends vertically below the lowerhorizontal boundary defined by of the MCL.

FIG. 6B provides a TEM (transmission electron microscopy) pictureshowing a lateral etched region in an exemplary multi-layeredcoilducting structure (e.g., layer 105). For the consistency ofreference, a lateral measurement approach is adopted in the definitionof the LBL thickness, a regional layer thickness of the lateralbyproduct layer is generally determined by the thickness measured alonga direction substantially parallel to the major surface of theunderlying substrate not visible in instant view). Particularly, FIG. 6Bdepicts a less than ideal structural outcome for a lateral byproductlayer over a lateral etched surface in a multi-layered conductingstnicture. For example, the LBL in the instant picture shows greatvariation in its thickness, particularly at the lower portion thereof(proximate the channel layer). In addition, the overall thickness of thebyproduct layer appears to be too large (e.g., more than 600 A).Moreover, the thicker log er portion appears to extend excessively belowa lower horizontal boundary defined by of the MCL, making it worryinglyclose to the channel layer.

FIG. 6C provides a TEM (transmission electron microscopy) pictureshowing a lateral etched region in another exemplary multi-layeredconducting structure (e.g., layer 105). Particularly, FIG. 6C depicts amore acceptable outcome for a LBL over the lateral etched surface of themulti-layered conductive structure. In the instant picture, theexemplary LBL appears more conformal in its thickness throughout itsvertical span without showing significant surface undulation (e.g.,fuzziness). However, the overall thickness of the byproduct layer stillappears too large (e.g., close to 600 A), and the lower portion thereofstill extends excessively below the lower horizontal boundary defined bythe MCL of the multilayered conducting structure.

FIGS. 7A-7C are schematic diagrams illustrating potential effects due tothe lateral byproduct layer profile.

FIG. 7A schematically illustrates a cross sectional diagram of a lateraletched surface covered by a thick and downwardly over-reaching byproductlayer. comparison, FIG. 7B schematically depicts a cross sectionaldiagram of a lateral etched surfitce covered by a thinner and more,confined byproduct layer. In each of the instant examples, themulti-layered conducting set cture of the exemplary semiconductor deviceis covered by two passivation layers. The inner passivation layercomprises substantially silicon oxide dielectric material, while theouter layer comprises substantially silicon nitride material. Also inthe instant example, copper is used as the middle conductive sub-layer.Accordingly, the exemplary LBL comprises substantially copper oxide.

During the channel activation/annealing process, the silicon nitridelayer would serve as a hydrogen reservoir, from which the hydrogenelements diffuse downward into the channel layer through the innersilicon oxide layer in a regulated, controlled fashion. As shown in FIG.7B, a slim and confined lateral byproduct layer may allow the hydrouendiffusion path to be substantially defined through the inner passiyationlayer (as illustrated by the downward arrow). However, as shown in FIG.7A, if a thick and oyer-extendinu lateral copper oxide layer is present,the porous copper oxide material may create a diffusion path of lesserresistance (as illustrated by the downward arrow), thus permittinghydrogen content to migrate there through with less regulation. As aresult, the electrical properties of the semiconductor device may beadversely affected, it is worth noting that, the existence of anundercut feature in the BBL of the multi-layered conducting structurewould make the abovementioned issue more announced, as an undercutstructure at the bottom portion of the lateral etch profile my give wayto the LBL, thereby allowing it to extend further downward toward thechannel region unobstructedly.

FIG. 7C shows a schematic plot diagram illustrating the thresholdvoltage characteristics corresponding to lateral byproduct layers ofdifferent thicknesses. Compared with a LEL having a more controlledprofile (e.g., thinner in overall thickness and more confined downwardextension, as illustrated in FIG. 7B), a thicker and over-extending LBL(as shown in FIG. 7A) may allow excessive diffusion of hydrogen contentinto certain regions of the channel layer, thereby shifting thethreshold voltage of the exemplary semiconductor device to the left(e.g., threshold voltage reduction). The reduction of threshold voltagemay result in higher leakage current through the channel region, therebyadversely impacting the performancelreliability of the device.

It is found that mindful process condition tuning during the passivationlayer deposition process (e.g., as depicted with respect to FIG. 5G) mayenable refinement in the profile of the LBL (e.g., the CuO byproductlayer) without substantially increasing fabrication complexity and lorincurring additional costs. With proper adjustments to the processconditions, it is possible to achieve a relatively regulated andconfined profile in the LBL (e.g., in terms of overall layer thickness,uniformity, and vertical extension). By way of example, certain initialprocess conditions during the PECVD process may play an important rolein dictating the outcome of the byproduct layer profile. For example, insome embodiments, a lower initial pressure condition may be appliedduring PECVD process to reduce the rate of chemical reaction at theexposed regions of the lateral etch pmfile in the multi-layeredconducting structure. Likewise, in some embodiments, the output powerduring initial phase of the PECVD process may be adjusted in accordancewith a disposed thickness of the passivation dielectric layer (e.g., ofsilicon oxide material). For instance, in some embodiments, an initialpower density setting for the PECVD process may be set at a lower levelfor a certain period of time until the disposed passivation layerreaches a first average thickness. A lower initial output power settingduring the passivation process may also help to reduce plasma damage tothe exposed portion of the lateral etched surface and contain theformation rate of the LBL. In some embodiments, a first passivationlayer of silicon oxide material is initially disposed at a first processcondition (with lower process parameters) for a first period of time toform an initial conformal dielectric layer of the exposed features of anexemplary semiconductor device (e.g., TFT device 100), and subsequentlyat one or more process conditions with higher setting parameters toexpedite the overall fabrication efficiency. It is noted that, in somescenarios (e.g., when a substantially regulated and confined LBL isprovided), the LBL may be overlooked when evaluating the featureproperties (e.g., feature geomety, such as taper angle and other featureprofile detemnnation) of the lateral etch profile in the multi-layeredconducting structure (e.g., second level conducting layer 105) toprovide the ease of device feature characterization.

FIGS. 8A-8B are schematic cross sectional illustrations of exemplarysemiconductor devices in accordance with some embodiments of the instantdisclosure.

FIG. 8A provides a schematic illustration of a substantially confinedLBL profile, in which a controlled vertical downward extension of theLBL achieved through proper process tuning. In the instant example, thelower portion of the LBL is kept at a reliable separation above a lowerboundaryfinterface defined between the BBL and the channel layer.Accordingly, the LBL is substantially free from reaching a lower layerboundary defined by the lower sub-layer (BBL) of the multi-layeredconducting structure (e.g., layer 105). In some embodiments, propertuning of the process conditions enables the dowmvard extension range ofthe LBL (e.g., the lowest observable tip) to be maintained substantiallyabove at least half the thickness of the BBL (i.e., the verticalseparation “h1” is larger than ½ the vertical thickness “h2” of theBBL). In this context, the thickness of the BBL may be measured at aregion proximate the lateral etch profile of the multi-layeredconducting structure. Nevertheless, in a typical embodiment where thethickness of the BBL maintains substantial uniformity, the average layerthickness of the BBL may be used as the detennination reference for thevertical spanning range of the LBL.

FIG. 8B provides a schematic illustration of a substantially regulatedLBL profile, in which a substantially thinner overall thickness withhigher layer uniformity is achieved through proper process tuning. Inthe instant embodiment, the lateral thickness uniformity of the LBL isdetermined by a three-point measurement approach, in which an averagevalue of a first LBL lateral thickness (e.g., t1), a second LBL, lateralthickness (e.g., t2), and a third LBL lateral thickness (e.g., t3) isadopted for the indication of LBL uniformity (i.e., (t1+t2+t3)/3).Particularly, the first lateral thickness t1 is measured substantiallyat the upper layer boundary defined by the MCL (substantiallycorresponds to the layer interface between TCL and MCL). The secondlateral thickness t2 is taken substantially at the mid-height locationof the MCL (i.e., substantially corresponds to the location of ½thickness of the MCL, where the MCL thickness may adopted an local or anaverage approach, comparable to that discussed previously). The thirdlateral thickness t3 is determined substantially at the lower layerboundary defined by the MCL (substantially corresponds to the layerinterface between MCL and BBL). In some entbodiments, proper tuning ofthe process conditions enables the three-point average of the LBLthickness to be maintained substantially within 400 A. In furtherembodiments, a local maximum lateral thickness in the LBL may beregulated within 400 A.

Accordingly, one aspect of the instant disclosure provides a method ofproviding a thin film transistor array panel. The method comprises:disposing a channel material layer over a substrate, the channelmaterial layer is provided with an oxide semiconductor material;disposing a lower sub-layer at least partially overlapping a verticalprojection defined by the channel material layer, the lower sub-layer isprovided with a conductive metal oxide material that includes indium andzinc, wherein the indium and zinc content in the bottom sub-layersubstantially defines a first indium to zinc content ratio; disposing amiddle sub-layer over the lower sub-layer, the middle sub-layer isprovided with a metal material; disposing an upper sub-layer over themiddle sub-layer, the upper sub-layer is provided with a conductivemetal oxide material that includes indium and zinc, wherein the indiumand the zinc content in the upper sub-layer substantially defines asecond indium tai zinc content ratio smaller than the first indium tozinc content ratio; patterning the multi-layered conductive structure togenerate a composite lateral etch profile therein, and disposing apassivation layer over the exposed region of the multi-layeredconductive structure and the channel material layer.

Accordingly, another aspect of the instant disclosure provides asemiconductor device comprises a multi-layered structure disposed over asubstrate and defining a composite lateral etch profile. Themulti-layered structure includes a lower sub-layer disposed over thesubstrate and comprising a metal oxide material that includes indium andzinc, the indium and zinc content in the bottom sub-layer substantiallydefining a first indium to zinc content ratio a middle sub-layerdisposed over the bottom sub-layer and comprising a metal material; anupper sub-layer disposed over the middle sub-layer and comprising ametal oxide material that includes indium and zinc, the indium to zinccontent in the upper sub-layer substantially defining a second indium tozinc content ratiO smaller than the first indium to zinc content ratio;and a lateral byproduct layer formed over the lateral etched surface,comprising substantially an metal oxide of the metal material in themiddle sub-layer. The lateral byproduct layer is substantially free fromreaching a lower layer boundary defined by the lower sub-layer, and athree point average thickness of the lateral byproduct layer is not morethan 400 A.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method of providing a thin film transistor array panel, comprising:disposing a channel material layer over a major surface of a substrate,the channel material layer comprising an oxide semiconductor material;disposing a lower sub-layer at least partially overlapping a verticalprojection defined by the channel material layer, the lower sub-layercomprising a conductive metal oxide material that includes indium andzinc, wherein the indium and zinc content in the bottom sub-layersubstantially defines a first indium to zinc content ratio; disposing amiddle sub-layer over the lower sub-layer, the middle sub-layercomprising a metal material; disposing an upper sub-layer over themiddle sub-layer, the upper sub-layer comprising a conductive metaloxide material that includes indium and zinc, wherein the indium and thezinc content in the upper sub-layer substantially defines a secondindium to zinc content ratio smaller than the first indium to zinccontent ratio; patterning the multi-layered conductive structure togenerate a composite lateral etch profile therein, and disposing apassivation layer over the exposed region of the multi-layeredconductive structure and the channel material layer.
 2. The method ofclaim 1, wherein the indium to zinc content ratio difference between thefirst and the third sub-layers is provided to be not less than 20%. 3.The method of claim 2, wherein patterning the multi-layered conductivestructure includes performing a wet etching process to concurrentlypattern the channel material layer, the lower, the middle, and the uppersub-layers.
 4. The method of claim 2, wherein the indium to zinc contentratio differentiation between the lower and the upper sub-layers affectsthe lateral etch profile, wherein a gap width associated with the etchprofile in the upper sub-layer is wider than a gap width associated withthe etch profile in the lower sub-layer.
 5. The method of claim 2,wherein disposing a passivation layer includes disposing a passivationlayer under an initial process condition at a first process parametersetting, and subsequently adjusting the process condition from the firstprocess parameter setting to a second process parameter setting, whereinthe process parameter tuning affects a profile of a lateral byproductlayer formed over the composite lateral etch profile from the laterallyexposed portion of the middle sub-layer.
 6. The method of claim 5,wherein disposing a passivation layer includes performing a chemicalvapor deposition process, wherein the first process parameter settingcorresponds to a first power density lower than a second power densitythat corresponds to the second process parameter setting.
 7. The methodof claim 5, wherein disposing a passivation layer includes implementingthe process parameter tuning to affect a profile of the lateralbyproduct layer such that the lateral byproduct layer is substantiallyfree from reaching a lower layer-boundary defined by the lowersub-layer.
 8. The method of claim 7, wherein the process parametertuning affects a profile of the lateral byproduct layer such that avertical extension of the lateral byproduct layer is maintained above atleast one half thickness of the lower sub-layer.
 9. The method of claim5, wherein disposing a passivation layer includes implementing theprocess parameter tuning to affect a profile of the lateral byproductlayer such that an average of lateral thickness along a directionsubstantially parallel to the major surface of the substrate thereof isnot greater than 400 A.
 10. The method of claim 9, wherein the processparameter tuning affects a profile of the lateral byproduct layer suchthat a local maximum lateral thickness thereof is not greater than 400A.
 11. The method of claim 1, further comprising disposing an additionalsub-layer between the channel material layer and the middle sub-layer,wherein the additional sub-layer comprises a metal oxide materialcontaining indium and zinc.
 12. The method of claim 11, whereindisposing an additional sub-layer includes disposing an additionalsub-layer in electrical contact with the channel material layer, whereinthe additional sub-layer is provided with an indium content higher thaneither one of the upper and the lower sub-layers.
 13. The method ofclaim 12, wherein a ratio between the indium content in the additionalsub-layer to the closer one of the upper and the lower sub-layers to thechannel material layer is in a range of more than 1 to about 1.5.
 14. Athin film transistor device, comprising: a multi-layered structuredisposed over a major surface of a substrate and defining a compositelateral etch profile, comprising a lower sub-layer disposed over thesubstrate, comprising a metal oxide material that includes indium andzinc, the indium and zinc content in the bottom sub-layer substantiallydefining a first indium to zinc content ratio; a middle sub-layerdisposed over the bottom sub-layer, comprising a metal material; anupper sub-layer disposed over the middle sub-layer, comprising a metaloxide material that includes indium and zinc, the indium to zinc contentin the upper sub-layer substantially defining a second indium to zinccontent ratio smaller than the first indium to zinc content ratio; and alateral byproduct layer formed over a lateral etched surface, comprisingsubstantially a metal oxide of the metal material in the middlesub-layer, wherein the lateral byproduct layer is substantially freefrom reaching a lower layer boundary defined by the lower sub-layerwherein an three point average thickness of the lateral byproduct layeralong a direction substantially parallel to the major surface of thesubstrate is not more than 400 A.
 15. The device of claim 14, whereinthe indium to zinc content ratio difference between the lower and theupper sub-layers is not less than 20%.
 16. The device of claim 14,wherein the indium to zinc content ratio differentiation between thelower and the upper sub-layers substantially affects a generation of anobliquely inclining lateral etched surface in the composite lateral etchprofile.
 17. The device of claim 16, wherein the inclining lateraletched surface is substantially smooth and linear.
 18. The device ofclaim 16, wherein the inclining lateral etched surface substantiallycorresponds to an inclining angle of about 40 degrees to about 85degrees with respect to a surface defined by the substrate.
 19. Thedevice of claim 15, wherein the indium to zinc content ratio in thefirst sub-layer is in a range from about 25% to about 80%.
 20. Thedevice of claim 19, wherein the indium to zinc content ratio in thefirst sub-layer is in a range from about 45% to about 70%.
 21. Thedevice of claim 15, wherein the indium to zinc content ratio in thethird sub-layer is in a range from about 5% to about 40%.
 22. The deviceof claim 21, wherein the indium to zinc content ratio in the thirdsub-layer is a in range from about 10% to about 35%.
 23. The device ofclaim 14, wherein the second sub-layer comprises at least one of analuminum, copper, manganese, molybdenum, and molybdenum tungsten (MoW)material.
 24. The device of claim 14, further comprising a channelmaterial layer at least partially overlaps a vertical projection of themulti-layered structure and in electrical contact there-with, whereinthe channel layer comprises at least one of an oxide semiconductor,elemental semiconductor, compound semiconductor, and alloy semiconductormaterial, in at least one of an amorphous, crystalline, andpoly-crystalline state.
 25. The device of claim 24, wherein the channelmaterial layer comprises at least one of an indium-gallium-zinc oxide(IGZO), indium-zinc-tin oxide (IZTO), indium-gallium-tin oxide (IGTO),and indium-aluminum-zinc oxide (IAZO) material.
 26. The device of claim24, further comprising an additional sub-layer arranged between thechannel material layer and the middle sub-layer, wherein the additionalsub-layer comprises a metal oxide material containing indium and zinc.27. The device of claim 26, wherein the additional sub-layer is arrangedproximate the channel material layer and in electrical contactthere-with, wherein the additional sub-layer comprises an indium contenthigher than that in each one of the upper and the lower sub-layers. 28.The device of claim 27, wherein a ratio between the indium content inthe additional sub-layer to the closer one of the upper and the lowersub-layers to the channel material layer is in a range of more than 1 toabout 1.5.